Hemorrhagic stroke may occur as a result of a subarachnoid hemorrhage (SAH), which occurs when a blood vessel on the brain's surface ruptures, leaking blood into the space between the brain and the skull. In contrast, a cerebral hemorrhage occurs when a defective artery in the brain bursts and floods the surrounding tissue with blood. Arterial brain hemorrhage is often caused by a head injury or a burst aneurysm, which may result from high blood pressure. An artery rupturing in one part of the brain can release blood that comes in contact with arteries in other portions of the brain. Even though it is likely that a rupture in one artery could starve the brain tissue fed by that artery, it is also likely that surrounding (otherwise healthy) arteries could become constricted, depriving their cerebral structures of oxygen and nutrients. Thus, a stroke that immediately affects a relatively unimportant portion of the brain may spread to a much larger area and affect more important structures.
Currently there are two major treatment options for cerebral aneurysm therapy, in either ruptured or unruptured aneurysms. One option is surgical clipping. The goal of surgical clipping is to isolate an aneurysm from the normal circulation without blocking off any small perforating arteries nearby. Under general anesthesia, an opening is made in the skull, called a craniotomy. The brain is gently retracted to locate the aneurysm. A small clip is placed across the base, or neck, of the aneurysm to block the normal blood flow from entering. The clip works like a tiny coil-spring clothespin, in which the blades of the clip remain tightly closed until pressure is applied to open the blades. Clips are made of titanium or other metallic materials and remain on the artery permanently. The second option is neurovascular embolization, which is to isolate ruptured or rupture-prone neurovascular abnormalities including aneurysms and AVMs (arterio-venous malformations) from the cerebral circulation in order to prevent a primary or secondary hemorrhage into the intracranial space.
Cerebrovascular embolization may be accomplished through the transcatheter deployment of one or several embolizing agents in an amount sufficient to halt internal blood flow and lead to death of the lesion. Several types of embolic agents have been approved for neurovascular indications including glues, liquid embolics, occlusion balloons, platinum and stainless steel microcoils (with and without attached fibers), and polyvinyl alcohol particles. Microcoils are the most commonly employed device for embolization of neurovascular lesions, with microcoiling techniques employed in the majority of endovascular repair procedures involving cerebral aneurysms and for many cases involving permanent AVM occlusions. Neurovascular stents may be employed for the containment of embolic coils. Other devices such as flow diversion implants or flow disruptor implants are used in certain types of aneurysms.
Many cerebral aneurysms tend to form at the bifurcation of major vessels that make up the circle of Willis and lie within the subarachnoid space. Each year, approximately 40,000 people in the U.S. suffer a hemorrhagic stroke caused by a ruptured cerebral aneurysm, of which an estimated 50% die within 1 month and the remainder usually experience severe residual neurologic deficits. Most cerebral aneurysms are asymptomatic and remain undetected until an SAH occurs. An SAH is a catastrophic event due to the fact that there is little or no warning and many patients die before they are able to receive treatment. The most common symptom prior to a vessel rupture is an abrupt and sudden severe headache.
Other vascular abnormalities may benefit from treatment with delivery of vascular implants. Aortic aneurysms are commonly treated with stent grafts. A variety of stents are used for the treatment of atherosclerotic, and other diseases of the vessels of the body. Detachable balloons have been used for both aneurysm occlusion and vessel occlusion.